Double-sided, edge-mounted stripline signal processing modules and modular network

ABSTRACT

A class of modular, double-sided, edge-mounted printed circuit (PC) board modules and an associated modular network architecture for constructing stripline signal processing networks including high-power analog amplifiers and beam forming networks for driving multi-beam antenna systems. The stripline signal processing networks are characterized by network elements constructed from defined-length segments of transmission media configured to exhibit precisely determined phase and impedance characteristics. These circuits may also include conventional passive “lumped” electrical elements, such as resistors, capacitors and inductors; non-linear circuit elements such as diodes; and active electrical elements, such as amplifiers and transistors.

TECHNICAL FIELD

The present invention relates to stripline signal processing systems forradio and microwave frequency applications and, more particularly,relates to a class of double-sided, edge-mounted printed circuit (PC)modules and an associated modular network architecture for constructingstripline signal processing networks including high-power analogamplifiers and beam forming networks for shaped beam and/or multi-beamantenna systems.

BACKGROUND OF THE INVENTION

Stripline signal processing circuits can be used to implement a varietyof analog signal operations on electromagnetic energy propagating withinthe circuit at radio frequency (RF) and microwave transmissionfrequencies. Generally stated, a stripline signal processing circuit, asthat term is used in this specification, is a circuit that includes oneor more transmission media segments of specified lengths and impedancecharacteristics, which are typically interconnected into a network, andwhich exhibit a desired frequency response (also called a “transferfunction”) that performs a desired signal processing operation onelectromagnetic energy propagating through the circuit. The term“microstrip” is commonly used to refer to stripline circuits having twoconductors in which the transmission media segments are exposed to oneor more dielectric materials on a first side backed by a conductingplane and one or more dielectric materials including air on a secondside without a second conducting plane. The term “tri-plate stripline”is commonly used to refer to stripline circuits that includetransmission media segments are exposed to one or more dielectricmaterials on both sides bounded by a conducting plane on each side. Inaddition, the terms “air microstrip” or “air stripline” are commonlyused to refer to stripline circuits in which the transmission mediasegments are exposed to air on both sides. All of these circuitconfigurations fall within the class of circuits referred to as“stripline” in this specification.

A stripline circuit often does, but does not necessarily, include one ormore lumped (also called “discrete” or “conventional”) electricelements, such as resistors, capacitors and inductors interconnectedwith the stripline segments within the circuit. These circuits may also,but need not necessarily, include active elements or stages such asactive amplifier stages, and non-linear elements such as diodes,transistors, and other conventional circuit elements. In addition, thesecircuits may also, but need not necessarily, include other types oftransmission media segments, such as coaxial cable, tubular waveguide,and so forth, as well as junctions between different types oftransmission media. Because the electromagnetic energy is processed bythe circuit as the signal propagates through the circuit, these circuitsare typically characterized by a network of stripline segments connectedbetween a plurality of input ports and a plurality of output ports, inwhich a desired signal processing operation is performed on the signalas it propagates from the input ports to the output ports.

Stripline signal processing circuits may be used to implement a widerange of functions, such as signal dividing, signal amplification,signal combining, signal encoding, and so forth. In general, they aretypically used to construct relatively simple functions or modules, asdescribed above, which are combined into more complicated structuresconfigured to implement higher-level components, such as beam formingnetworks, hybrid matrix amplifiers, radio frequency amplifiers, and soforth. These higher-level components, in turn, may be interconnected andcontrolled to implement a wide range of commercial devices, such asradars for missiles and missile defense, satellite communicationsystems, wireless telephone base station antennas, Doppler radars, andmany others.

Stripline signal processing circuits are typically referred to as“reciprocal” when the transfer function is the same for a signalpropagating from the input ports to the output ports as it is for asignal propagating from the output ports to the input ports. Reciprocalsignal processing circuits are particularly well suited for use in radarsystems that both emit and receive electromagnetic energy through thesame transmission path. Orthogonal signal processing circuits are aparticularly important class of signal processing circuits that arecharacterized by a plurality of input ports that are isolated from eachother. This allows the signal injected into each input port to beindependently controlled without substantial interference from the otherinput ports. Reciprocal orthogonal circuits, even more specifically, arean important class of signal processing circuits that are well suited toa range of applications using analog amplifiers and beam formingnetworks. The reciprocity property can be obtained through the reuse ofa portion or all of a passive circuit for bidirectional signal flow.

As noted above, an orthogonal circuit includes a number of isolatedinput ports, and also typically includes a plurality of output portsthat each receive a weighted, phase-adjusted combination of the inputsignals injected into the input ports. That is, the output signal ateach output port typically includes a linear combination or“superposition” of input components, in which each input component is anamplitude-weighted, phase-adjusted portion or division of the signalinjected into one of the input ports. In other words, the input signalsare isolated from each other, and each input signal is divided into anumber of weighted and phase-adjusted components that are delivered tothe output ports, such that each output port produces an amplitudeweighted and phase-adjusted linear combination of the input signals. Inaddition, the input and output impedances of the orthogonal circuit aretypically matched across connecting junctions or ports so that the idealnon-absorbing circuit is theoretically lossless for signal flow betweenports. That is, the orthogonal circuit does not absorb or reflect backany of the energy injected into the input ports, but instead divides anddelivers all of the input energy to the output ports, where they arecombined into amplitude weighted, phase-adjusted linear combinations ofthe input signals.

Hybrid circuits are a subclass of orthogonal signal processing networkscharacterized by two inputs, two outputs, and a division of energy fromeach input port to the output ports. The term “hybrid junction”typically refers to a hybrid circuit in which there is an equal divisionof power from each input port to the output ports. A “hybrid coupler,”on the other hand, typically refers to a hybrid circuit in which thepower division is generally unequal. A hybrid junction in which thephase shift from each input port to the two output ports is zero degrees(0°) and ninety degrees (90°), respectively, is known as a “quadrature”junction or circuit; and a hybrid junction in which the phase shift fromeach input port to the two output ports is zero (00) degrees andone-hundred eighty degrees (180°), respectively, is known as a “magic T”junction or circuit. These circuits are also otherwise known as 0°/90°and 0°/180° hybrids. These well known building blocks are usuallyreciprocal and form the basic building blocks for constructinghigher-level orthogonal circuits, which are often referred to as hybridmatrices, Butler matrices, beam forming networks, hybrid matrixamplifiers, RF amplifiers, diplexers, monopulse comparators, and soforth. These building blocks can be used in conjunction with other typesof junctions including non-isolating reactive tee junctions and can beused with various types of phase or time delay elements or components.

More particularly, a Butler matrix is a type of higher-level reciprocalorthogonal passive circuit characterized by an equal number of inputports and output ports, and equal power division of each input signal tothe several output ports. The Butler matrix circuit provides equal powersignal amplitudes delivered to each output port. A three-by-three Butlermatrix includes three input ports and three output ports, a four-by-fourButler matrix includes four input ports and four output ports, aneight-by-eight Butler matrix includes eight input ports and eight outputports, and so forth. In addition, other well known circuits and circuitcomponents can be constructed from hybrid junctions and other componentssuch as phase shifters and resistors used for impedance matching and foranalog signal processing. For example, monopulse comparators, diplexers,analog amplifiers, and beam steering circuits can be constructed in thismanner. An important example of such a circuit is a high-level Butlermatrix, which may be used to implement beamforming networks (BFNs) formulti-beam antenna systems with a large number of beams. Thesehigh-level Butler matrices may be constructed from complexes offour-by-four Butler matrices, which in turn may be constructed fromcomplexes of hybrid junctions and other circuit elements, such as phaseshifters.

For constructing high-level Butler matrices using hybrid junctions, see“Multiple Beams from Linear Arrays” by J. P. Shelton and K. S. Kelleher,published in the March 1961 “IRE Transactions on Antennas andPropagation.” For constructing monopulse comparators using hybridjunctions, see “A Wide-Band Monopulse Comparator With Complete Nullingin All Delta Channels Throughout Sum Channel Bandwidth” by Kian Sen Ang,Yoke Choy Leong and Chee How Lee, published in the February 2003 “IEEETransactions on Microwave Theory and Techniques.” For constructingdiplexer circuits using hybrid junctions, see “A Diplexer Using HybridJunctions” by Leon J. Ricardi published in the August 1966 “IEEETransactions on Microwave Theory and Techniques.” For constructinghybrid matrix amplifiers (HMAs) using hybrid junctions, see “MultiportPower Amplifiers For Mobile-Radio Systems Using Microstrip ButlerMatrices” by A. Angelucci, P. Audagnotto, P. Corda, and B. Piovano,published in the June 1994 Antennas and Propagation Society IntentionalSymposium. Those skilled in the art will appreciate that other devices,and in particular more complicated HMAs and beam forming networks formulti-beam antenna systems, may be constructed using the principles andtechniques taught in this specification and in the documents referencedabove, which are incorporated herein by reference.

In particular, hybrid junctions form the basic building blocks for thebeam forming networks that are used in shaped beam and/or multi-beamantenna systems having a wide range of applications including, but notlimited to, antennas for wireless telephone base stations, radars,missile guidance systems, missile defense systems, satellitesurveillance systems, and satellite communication systems. In general,component beams may be pointed in different directions so to allow forsubstantially isolated input ports corresponding to each component beam.Component beams can be combined in various ways to form composite beams.Each beam may be encoded with beam-specific information and combiningcan occur for analog or digital signals.

To create these capabilities, the multi-beam antenna system includes abeam forming network or circuit that transfers signal energy from one ormore input ports to a plurality of output ports operatively connected toone or more antenna elements to emit or receive the desired beams.Although the most critical design considerations may vary fromapplication to application, it is generally desirable to manufacturebeam forming networks that are inexpensive and easy to manufacture,repeatable in performance characteristics, light in weight, small insize, reliable and durable in construction, low in RF signal losses, lowin noise generation, easy to ground properly, and easy to maintain.Although other design objectives may also be important in a particularapplication, this list includes many of the most important designconsiderations for many applications.

A number of these design objectives can be satisfied by manufacturingthe signal processing circuits on printed circuit (PC) boardsconstructed from a dielectric substrate and using stripline carried onthe dielectric substrate as the transmission media. The dielectricsubstrate typically has a ground plane attached to one side and thestripline carried on the other side. This configuration produces acircuit that can be mass produced on a PC board using conventionaletching technology and processes. The resulting device exhibits lowmanufacturing costs, reliability, durability, repeatable performancecharacteristics, and accessible and solid ground characteristics. Thesecircuits can be readily designed to exhibit low RF signal losses and lownoise generation. The drawback in using this construction paradigm isthat beam forming networks using hybrid junctions are oftencharacterized by crossover points in which stripline segments must passby each other physically without interfering with each otherelectrically.

On a PC board, the need for crossovers presents a design challengebecause the stripline segments must remain physically separated fromeach other to avoid electrical interconnection (if the striplinesegments physically touch each other) or radiating interference orcross-talk (if the stripline segments come too close together withoutphysically touching each other). A number of techniques have beendeveloped to implement crossovers for stripline signal processorsimplemented on PC boards, such as “flying bridge” sections of PC boardthat physically jump one stripline segment over another, coaxial cablelinks to cross each other, and multiple layered PC board constructs withconductors suspended in air and extending between PC boards to implementcrossovers. Each of these designs increases the cost of the circuit,reduces the physical ruggedness of the circuit, and has the potential toincrease noise generation and RF signal loss, particularly at junctionsbetween different types of transmission media segments. Moreimportantly, these somewhat clumsy solutions to the crossover problemgreatly complicate the manufacturing process because the entire circuitcannot be arranged on a single PC board using stripline transmissionmedia segments formed into the PC board that can then be manufacturedthrough a conventional etching techniques and processes.

Another technique employs a circuit known as a “zero-dB crossover”that-can be comprised of two cascaded quadrature hybrid junctions.Although this type of crossover can be implemented on a single flat PCboard without physical trace jumps, it occupies a relatively largesection of PC board space. Because the crossover is a basic buildingblock that is repeated many times in creating a higher-level beamforming network, the significant board size required to implement thezero-dB crossover quickly multiplies into an overly large and expensivePC board as the complexity of the bream forming network increases.

In addition to the problem of crossovers, stripline signal processingcircuits arranged on PC boards must maintain proper physical spacingbetween the stripline segments to avoid radiating interference. Further,designing each stripline segment to have a precisely determined phasecharacteristic at RF and microwave operational frequencies also requiresthe stripline circuit to be physically arranged on the printed circuitboard in a manner that consumes a relatively large amount of planarboard space. To maintain proper spacing and minimize the number ofcrossovers required, and to take advantage of the natural symmetry ofthe circuits, they are typically arranged out linearly, with the inputsports spaced along one side and the output ports spaced along the otherside of the stripline circuit. The transfer function of the striplinecircuit then processes the signal as it propagates across the PC boardfrom the input ports to the output ports.

For this type of circuit configuration operating at a carrier frequencyof 1.92 GHz (which is the center frequency of the authorized PCSwireless telephone band), a conventional hybrid junction layouttypically occupies PC board space that is approximately one quarter of asquare wavelength “in the guide” (λ_(g)) (e.g., an approximately squaresection of PC board that is λ_(g)/2 in length on each side). A typicaldielectric material (e.g., PTFE Teflon®) having a dielectric constantequal to 2.2 (ε_(r)=2.2) can be used to construct PC boards that willexhibit an effective dielectric constant of 1.85 (ε_(reff)=1.85) formicrostrip transmission media segments exposed to the PC board on oneside and exposed to air on the other side. For this type of PC boardcircuit, the wavelength in the guide (λ_(g)) (i.e., the wavelength aspropagating in the stripline transmission media as laid out on the PCboard with one side exposed to the dielectric substrate and the otherside exposed to air) is approximately 4.52 inches (11.48 cm), whichresults in a side dimension of the PC board required to implement aquadrature hybrid junction of approximately 1.13 inches (2.87 cm). It iswell known to someone familiar with the art that using a substratematerial having a higher dielectric constant value can reduce theoverall size of the circuit. Materials with substantially higherdielectric constant values can be substantially more expensive, can havehigher RF signal losses, and can have RF power handling limitations thatare a lower value due to reduced stripline trace width values. It isdesirable to have a circuit with sufficiently wide conducting tracewidth values and low RF signal loss characteristics for conditions ofmoderate to high operational RF power levels. Generally, the use of asubstrate material with a low dielectric constant value is oftendesirable when RF power levels are a significant design consideration.

Using this technology and connecting four hybrid junctions together toconstruct a four-by-four Butler matrix occupies PC board space that isapproximately one square wavelength in the guide (λ_(g)), which at acarrier frequency of 1.92 GHz results in a side dimension of the PCboard required to implement the four-by-four Butler matrix of at least4.52 inches (11.48 cm) using microstrip on a dielectric material havinga dielectric constant equal to 2.2 (ε_(r)=2.2). The physical size of thePC board starts to become unwieldy and expensive as the number of hybridjunction elements increases beyond the eight to 16 element level. Forexample, a 64×64 Butler matrix requires 48 hybrid junctions andassociated crossovers, and a 128×128 Butler matrix requires 160 hybridjunctions and associated crossovers. Arranging a stripline signalprocessing circuit on a planar PC board in the conventional manner forthese circuits would result on a very large PC board that would be veryexpensive to manufacture and install in a secure manner.

An approach to solving some of the problems associated with PC boardstripline signal processing circuit design is provided in Tanaka et al.,U.S. Pat. No. 6,252,560, which describes a four-by-four Butler matrixthat is arranged on a double-sided dielectric PC board with a groundplane located in the center. See Tanaka at FIG. 7. This allows the firststage hybrid junctions to be carried on a first side of the double-sideddielectric PC board, and the second stage hybrid junctions to be carriedon the other side of the double-sided dielectric PC board. Crossoversare conveniently implemented using tap-through connections between thestripline circuits located on opposite sides of the PC board. Thisprovides an elegant, low noise and space effective mechanism forimplementing the crossovers. However, the circuit is still laid outlinearly with the input ports located on the other side of the circuitfrom the output ports. In addition, the Tanaka reference shows theButler matrix implemented on a common board with a power divider networkfeeding a set of patch radiators. Tanaka does not teach or suggestfurther steps to reduce the physical size of the Butler matrix circuit.Nor does it teach or suggest mechanisms for minimizing the PC boardspace required to implement higher-order analog signal processingcircuits.

Accordingly, a continuing need exists for stripline signal processingnetworks that are inexpensive and easy to manufacture, repeatable inperformance characteristics, light in weight, small in size, reliableand durable in construction, low in RF signal losses, low in noisegeneration, easy to ground properly, and easy to maintain. Morespecifically, a need exists for improvements in stripline signalprocessing circuit design that reduce the PC board space required toimplement higher-order stripline signal processing circuits.

SUMMARY OF THE INVENTION

The present invention meets the needs described above in double-sided,edge-mounted modular printed circuit (PC) boards and an associatedmodular network architecture for constructing stripline signalprocessing networks including high-power analog amplifiers and beamforming networks (BFNs) for use in shaped beam and/or multi-beam antennasystems. Each module is manufactured from a double-sided dielectriccircuit board with a ground plane located in the center. Unlike priordouble-sided PC board deigns, however, the present invention includesinput and output interface ports along a common interface edge definedby one or both sides of the double-sided circuit board. This allowsnon-crossing circuit portions to be carried on each side of thedouble-sided circuit board, with crossovers implemented with tap-throughconnections between the circuit portions, and input-output ports locatedalong the interface edge, to create an edge-mounted system forconstructing modular signal processing networks from a system ofdouble-sided, edge-mounted modules.

Typically, a first stage of the circuit extends linearly away from inputports located at the interface edge, tap-through connectors participatein the implementation of crossovers to a second stage of the circuitlocated on the other side of the double-sided PC board. The second stagecircuit then extends back toward output ports, which are also located atthe interface edge. In this manner, the first and second stages of thecircuit overly each other on opposite sides of the double-sided PCboard, and all input and output ports are located along a commoninterface edge. In addition, the circuit portions themselves, typicallyhybrid junctions and circuit portions that include complexes of hybridjunctions, may include sinuous stripline trace elements that reduce thelength of the PC board in a desired dimension. For example, first andsecond stage complexes of hybrid junctions may be laid out using sinuoustrace elements to minimize the depth of the PC board extending away fromthe interface edge.

The results is a compact, edge-mounted, double-sided, modular signalprocessing PC board design that is well suited to assemblinghigher-order circuits from complexes of lower-order, edge-mountedmodules. This architecture may be used to construct hybrid matrixamplifiers (HMAs) and beam forming networks for multi-beam antennasystems that exhibit many advantages over prior HMA and beam formingnetworks including decreased size, decreased cost, standardization ofmodule design, scalability, repeatability of manufactured products, easeof construction, and ease of repair and maintenance. Circuitconfigurations implemented in this manner can also be readily configuredto exhibit low noise generation, low power and signal losses, and ruggedphysical construction.

Generally described, the invention may be implemented as a striplinesignal processing module that includes a first planar dielectricsubstrate that defines an edge, a second planar dielectric substratethat defines an edge, and a ground plane. The first dielectricsubstrate, the second dielectric substrate, and the ground plane areadhered together in an overlaying configuration with the ground planelocated between the first and second dielectric substrates and the edgesaligned to form an interface edge. A first stripline circuit is carriedon the first dielectric substrate, and a second stripline circuit iscarried on the second dielectric substrate. The module also includes oneor more input ports and one or more output ports located at theinterface edge and electrically connected to the first or secondstripline circuits. The first and second stripline circuits areconfigured to receive propagating signals at the input ports, perform asignal processing operation on the received propagating signals, anddeliver processed signals to the output ports.

Typically, the first dielectric substrate, the second dielectricsubstrate, and the ground plane are approximately coextensive in theirplanar dimensions to form a double-sided dielectric PC board with aconducting ground plane sandwiched in the middle. In addition, the firstand second stripline circuits are typically constructed from striplinethat is exposed to the dielectric substrate on one side and exposed toair on the opposite side. The module may also include one or moreelectrical connections between the first and second stripline circuits,which are typically implemented as tap-through connectors passingthrough and insulated from the ground plane. Further, the first andsecond stripline circuits may be non-crossing, and the electricalconnections between the stripline circuits may participate in theformation of crossovers connecting the stripline circuits to formorthogonal signal processing circuits, such as circuits comprised ofhybrid junctions.

In particular, the first and second stripline circuits may implementfirst and second stage orthogonal beam forming networks, respectively,that are combined to form a multi-stage orthogonal beam forming network.For example, the multi-stage orthogonal beam forming network may be atwo-by-four beam steering circuit, a diplexer filter circuit with atleast three ports, a three-by-three Butler matrix circuit, afour-by-four Butler matrix circuit, an eight-by-eight Butler matrixcircuit, a four-by-four monopulse comparator circuit, a three-by-fourmonopulse comparator circuit, an eight-by-eight monopulse comparatorcircuit, or a three-by-twelve monopulse comparator circuit, and otherlike constructions. These modules may then be combined to constructhigher-order machines; such as HMAs and beam forming networks for shapedbeam and/or multi-beam antennas.

For all of these modules, the stripline circuits may include one or moresinuous trace legs configured to exhibit a desired phase and impedancecharacteristic while reducing the displacement of the trace in aselected dimension. For example, the first and second stripline circuitsmay implement a four-by-four Butler matrix circuit configured for anoperational carrier frequency, in which the planar dimensions of thefirst dielectric substrate, the second dielectric substrate, and theground plane are less than one and one-half times the wavelength of thecarrier frequency in the strip transmission media. More specifically,the planar dimensions may include a length dimension in the direction ofthe interface edge that is less than one and one-half times thewavelength of the carrier frequency in the guide; and a width dimensionperpendicular to the interface edge that is less than one-half times thewavelength of the carrier frequency in the guide. Even moreparticularly, the length may be approximately equal to the wavelength ofthe carrier frequency in the strip transmission media, and the width maybe approximately one-fourth times the wavelength of the carrierfrequency in the strip transmission media.

The invention may also be embodied as a modular stripline signalprocessing network including an interconnected set of network modules,in which each network module includes a first stripline circuit locatedon a first side of a double-sided dielectric substrate board, a secondstripline circuit located on a second side of the double-sideddielectric substrate board, and one or more input ports and output portslocated along an interface edge defined by the dielectric substrateboard. In this case, each network module is configured to receivepropagating signals at the input ports, perform a signal processingoperation on the received propagating signals, and deliver processedsignals to the output ports.

The interface ports for each network module, as described above, may beedge-connected to another network board through soldered connections.Alternatively, they may be configured for removable edge-connection toanother network board through separable connections, for example byimplementing the interface ports as blind-mate coaxial connectors.Typically, each network module implements a lower-order hybrid junctioncircuit, and the interconnected set of network modules combines thenetwork modules to implement a higher-order hybrid junction circuit. Forexample, each lower-order hybrid junction circuit may be athree-by-three, a four-by-four, or an eight-by-eight Butler matrixcircuit. And the higher-order hybrid junction circuit may include atleast sixteen input ports and sixteen output ports. For example, thehigher-order hybrid junction circuit may be a 64×64 or 128×128 Butlermatrix used as a beam forming network for a multi-beam antenna.Alternatively, the higher-order hybrid junction circuit may be amulti-stage high-power HMA including scores of hybrid junctions. Manyother end products may be constructed using the modular, edge-connected,double-sided dielectric PC board configuration enabled by the presentinvention.

In view of the foregoing, it will be appreciated that the presentinvention avoids the drawbacks of prior methods for implementingstripline signal processing circuits, such as analog amplifiers and beamforming networks, on PC boards. The specific techniques and structuresfor creating stripline signal processing modules, and higher-ordermodular signal processing networks constructed from complexes oflower-order network modules, and thereby accomplishing the advantagesdescribed above, will become apparent from the following detaileddescription of the embodiments and the appended drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a multi-beam antenna system including amodular beam forming network embodying the present invention.

FIG. 2 is a block diagram of a vertical electrical downtilt antennasystem including a modular beam forming network embodying the presentinvention.

FIG. 3A is a perspective view of a conceptual design for a double-sided,edge-mounted stripline signal processing module.

FIG. 3B is a perspective view of an alternate conceptual design for adouble-sided, edge-mounted stripline signal processing module.

FIG. 4 is a perspective exploded view of a double-sided, edge-mountedstripline signal processing module.

FIG. 5A is a functional block diagram of a two-by-four beam formingnetwork for use in a single-beam vertical electrical downtilt antennasystem.

FIG. 5B is a circuit board layout diagram of the back side portion of adouble-sided, edge-mounted stripline signal processing moduleimplementing the two-by-four beam forming network shown in FIG. 5A.

FIG. 5C is a circuit board layout diagram of the front side portion ofthe two-by-four beam forming module shown in FIG. 6A.

FIG. 6A is a functional block diagram of an alternate embodiment of atwo-by-four beam forming network for use in a single-beam verticalelectrical downtilt antenna system.

FIG. 6B is a circuit board layout diagram of the back side portion of adouble-sided, edge-mounted stripline signal processing moduleimplementing the two-by-four beam forming network shown in FIG. 6A.

FIG. 6C is a circuit board layout diagram of the front side portion ofthe two-by-four beam forming network filter module shown in FIG. 6A.

FIG. 7A is a functional block diagram of a four-by-four Butler matrixmodule.

FIG. 7B is a circuit board layout diagram of the back side portion of adouble-sided, edge-mounted stripline signal processing moduleimplementing the four-by-four Butler matrix circuit shown in FIG. 7A.

FIG. 7C is a circuit board layout diagram of the front side portion ofthe four-by-four Butler matrix module shown in FIG. 7A.

FIG. 8A is a functional block diagram of a monopulse comparator module.

FIG. 8B is a circuit board layout diagram of the back side portion of adouble-sided, edge-mounted analog signal processing module implementingthe monopulse comparator module shown in FIG. 8A.

FIG. 8C is a circuit board layout diagram of the front side portion ofthe monopulse comparator module shown in FIG. 8A.

FIG. 9 is a functional block diagram of an eight-by-eight Butler matrixmodule.

FIG. 10A is a circuit board layout diagram of the back side portion of adouble-sided, edge-mounted analog signal processing module implementingthe eight-by-eight Butler matrix circuit shown in FIG. 9.

FIG. 10B is a circuit board layout diagram of the front side portion ofthe eight-by-eight Butler matrix module shown in FIG. 9.

FIG. 11A is a conceptual diagram of an edge-mounted modular striplinesignal processing network for implementing an eight-by-eight Butlermatrix from two four-by-four Butler matrix modules and a third moduleimplementing four hybrid junctions that are each daughter boards edgemounted to a mother board.

FIG. 11B is a functional block diagram of an eight-by-eight Butlermatrix illustrating the division of signal processing functions amongthe modules shown in FIG. 11A.

FIG. 12 is a conceptual diagram of tree-type stripline signal processingnetwork comprising a system of daughter boards edge mounted to motherboards.

FIG. 13 illustrates a modular stripline signal processing networkincluding daughter boards edge mounted to a mother board using separableblind-mate coaxial connectors.

FIG. 14 is a logic flow diagram illustrating a process for designing amodular stripline signal processing network.

FIG. 15A is perspective exploded view of a tri-plate stripline modulefor a modular stripline signal processing network.

FIG. 15B is a side view of a first stripline circuit of the tri-platestripline module of FIG. 15A.

FIG. 15C is a side view of a second stripline circuit of the tri-platestripline module of FIG. 15A.

FIG. 15D is an assembled perspective view of the tri-plate stripline ofFIG. 15A.

FIG. 16A is a functional block diagram of a diplexer filter module.

FIG. 16B is a circuit board layout diagram of the back side portion of adouble-sided, edge-mounted analog signal processing module implementingthe diplexer filter module shown in FIG. 8A.

FIG. 16C is a circuit board layout diagram of the front side portion ofthe i diplexer filter module shown in FIG. 16A.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention relates to a class of double-sided, edge-mountedprinted circuit (PC) modules and an associated modular networkarchitecture for constructing stripline signal processing networksincluding high-power analog amplifiers and beam forming networks for usein multi-beam antenna systems. The stripline signal processing networksare characterized by network elements constructed from defined-lengthsegments of stripline configured to exhibit precisely determined phaseand impedance characteristics. These circuits may also includeconventional passive “lumped” electrical elements, such as resistors,capacitors and inductors; non-linear circuit elements such as diodes;and active electrical elements, such as amplifiers and transistors.

The stripline segments are typically constructed from conductivestripline, such as tin-covered copper traces, carried on a dielectric PCboard substrate constructed from, for example, PTFE Teflon® laminateimpregnated with glass fibers. Although other types of dielectric PCboard substrates may be used, this particular substrate exhibitsdesirable dielectric, cost, hardness, durability, consistency andetching characteristics that makes it well suited to mass producing PCboards for relatively low cost, high-production applications, such aswireless telephone base station antennas and similar applications. Adouble-sided PC board can be readily manufactured by using a dielectricadhesive layer to adhere a first PC board carrying an attached groundplane to a second PC board without an attached ground plane to create anintegral double-sided dielectric PC board with a ground plane sandwichedin the middle.

Large planar sheets of this material may then be mass produced, etchedand cut into multiple PC boards or modules in which each resultingmodule has two sides of dielectric PC board, each carrying an etchedstripline circuit, and a center ground plane. Typically, the dielectricPC board sides and the center ground plane are cut with a common die,and as a result are substantially coextensive in planar dimensions. Formany applications, the stripline circuits on each side of the board maybe non-crossing and formed entirely of etched stripline, which avoidsthe need for coaxial links, “flying bridge”, “air bridge”, “zero dBcrossover”, or other devices to implement crossovers that might addnoise, increase size, cost and fragility to the board. Connectionsbetween stripline circuits located on either side of the board aretypically implemented through tap-through connectors, and the input andoutput ports are located-along a common interface edge. In addition, forsome applications the modules may include connection points forsolder-mounting discrete electrical elements, such as resistors,capacitors, inductors, diodes, transistors, and amplifiers into thestripline circuits.

A variety of standard and special purpose “lower-level” modules, such asquadrature hybrids, diplexer filters, amplifier power dividers,amplifier crossovers, monopulse comparators, Butler matrix circuits, andcustomized beam forming networks may be constructed in bulk this manner.These modular components may then be assembled together in anedge-mounted “tree” configuration to create higher-level striplinesignal processing machines, such as high-power hybrid matrix amplifiers,other types of RF amplifiers, beam forming networks for multi-beamantenna systems.

In particular, lower-level orthogonal circuit modules with well-knownproperties, such as Butler matrices, quadrature hybrids, “magic-T”hybrids, and monopulse comparators may be mass produced inexpensively,with tight performance tolerances, and with desirable size, ruggednessand durability qualities. These basic building blocks of bi-directionalsignal processing systems implemented in double-sided, edge-mountedmodules may then assembled to construct higher-order signal processingnetworks. These higher-order networks, in turn, provide the signalprocessing network infrastructure required to assemble a wide range ofcommercially and scientifically important high-power and multi-beamssystems, such as multi-beam Doppler radar systems, multi-beam missiledefense systems, missile guidance systems, satellite reconnaissancesystems, satellite communication systems, and the like. Those skilled inthe art will appreciate that the standardization of the basic buildingblocks of orthogonal signal processing systems into double-sided,edge-mounted modules that can be inexpensively mass produced and readilyassembled into higher-order signal processing machines represents amajor advance in this particular technology.

Further, the modular design of complex multi-beam and high-poweramplifier using standardized double-sided, edge-mounted modules withnon-crossing stripline circuits on each side of the PC board andcross-board connections implemented through tap-through connectorsexhibit other desirable design characteristics. For example, the modulesmay be edge-connected together with separable connectors, such asblind-mate coaxial connection to allow easy removal and replacement ofindividual components. The “tree” nature of edge-connected moduleconstruction produces a three-dimensional processing unit, as opposed toa huge planar configuration, which is easier to move and install,reduces the required bracing, reduces the weight, reduces wind and dragconcerns for outdoor installations, and provides inherent ventilationcorridors within the three-dimensional processing unit. Basically, thedouble-sided, edge-mounted modular allows much more processingcapability to be manufactured and installed, much less expensively,within in any given physical envelope.

In addition, the conducting ground plane located in the middle of thedouble-sided dielectric board isolates the circuits on either side ofthe board from radiating interference from each other, which allows thecircuits to be located close to each other in space yet maintainelectric isolation. The ability to deploy the stripline circuits in eachside of the board in non-crossing configurations, which crossoversimplemented with tap-through connections, produces a low-noise, low-lossand rugged board design. The use of edge-connected I/O further reducesthe cost and simplifies the design of the modular systems by avoidingthe need for free spans of conductors, coaxial cable or other types oflinks between boards other than the edge connections located atedge-mounted junctions between boards.

The inventor of the present system has also developed a technique forusing sinuous stripline traces to reduce the size of modules in adesired planar dimension. This innovation, combined with thedouble-sided, edge-mounted board design, enables compaction of planarstripline signal processing PC board circuits to an extent that has notbeen achieved before for circuit constructions using low dielectricconstant substrate materials. For a particular example, the conductivestripline transmission media segments may be formed into the PC boardusing a conventional PC board etching technique. The PTFE Teflon®dielectric material exhibits a dielectric constant equal to 2.2(ε_(r)=2.2), which results in stripline segments exposed to the PC boardon one side and exposed to air on the other side exhibiting an effectivedielectric constant of 1.85 (ε_(r)=1.85). For this type of PC boardcircuit operating at a carrier frequency of 1.92 GHz (the center of theauthorized PCS wireless telephone band), the wavelength in the guide(λ_(g)) (i.e., the wavelength as propagating in the stripline as carriedon the PC board with one side of the stripline exposed to the dielectricsubstrate and the other side exposed to air) is approximately 4.52inches (11.48 cm), which results in a side dimension of the PC boardrequired to implement a hybrid junction in a conventional planar layoutof approximately 2.26 inches (5.74 cm). Using planar technology andconnecting four hybrid junctions together to construct a four-by-fourButler matrix occupies PC board space that is approximately one squarewavelength in the guide (λ_(g)), which results in a side dimension ofthe PC board required to implement the four-by-four Butler matrix of4.52 inches (11.48 cm). It will be appreciated that the wavelengthschange for different carrier frequencies and for PC board substrateswith different dielectric constant values, for surrounding media otherthan air, and for configurations in which a dielectric material islocated on both sided of the stripline circuit, which could beimplemented for the entire board or for selected segments. For thisreason, the board dimensions are preferably expressed as multiples ofλ_(g) rather than absolute lengths.

Using the sinuous stripline traces combined with the double-sided,edge-mounted board design allows a four-by-four Butler matrix to beimplemented on a board that that is approximately λ_(g) (i.e., 4.52inches or 11.48) cm along the interface edge, but is only λ_(g)/4 (i.e.,1.13 inches or 2.27 cm) in the direction extending away from theinterface edge. This represents a reduction to one-forth the board sizeof that required to implement the four-by-four Butler matrix using theconventional layout. For a mass -produced, highly price sensitive item,such as wireless telephone base station antennas, this reduction inboard size alone represents a significant cost advantage. Thisadvantage, together with the other benefits of the modular design,including the elegant, low-noise, low-loss crossover implementationthrough tap-through connections, low cost, small size, low weight, andease of manufacturing result in a major improvement in stripline signalprocessing circuit design.

Turning now to the figures, in which similar reference numerals indicatesimilar elements in the several figures, FIG. 1 is a block diagram of amulti-beam antenna system 100 including a modular beam forming network102 embodying the present invention. As noted above, many differenttypes of stripline signal processing modules and modular systems may beconstructed using the double-sided, edge mounted PC board modulartechnology of the present invention. Multi-beam antenna systems are aimportant class-of these system, which can be used to drive wirelessbase station antennas, Doppler radar systems, satellite communicationsystems, missile defense and guidance systems, and a range of otherdevices that are generally characterized by a plurality of voltagesources 104 feeding a modular, double-sided, edge-mounted stripline beamforming network 102, which in turns drives an antenna array 106 toproduce multiple beams 108. In general, each of these beams may includea beam component from each of the voltage sources 104, and may beindependently steered and encoded with information. Also, each of thesebeams may be combined to form one or more composite beams that canproduce a “shaped beam” coverage pattern.

FIG. 2 is a block diagram of a vertical electrical downtilt (“VED”)antenna system 200, which is simplified single-beam variant similar tothe multi-beam antenna system 100. This system includes a pair ofcomplimentary voltage sources 204 that typically produce in-phasevoltage signals that vary in magnitude inversely in proportion to eachother. That is, the voltage sources 204 a and 204 b are typically inphase with each other throughout the range of control, and the amplitudeof voltage source 204 a increases proportionately as the amplitude ofvoltage source 204 b decreases, and vice versa, in a complimentaryfashion throughout the range of control. Typically, this type ofcomplimentary voltage source pair can be generated by splitting a singleconstant-amplitude voltage signal into two channels and varying thepower division between the two channels. The pair of complimentaryvoltage sources 204 feeds a modular, double-sided, edge-mounted verticalelectrical downtilt network 202. This network produces antenna drivesignals that cause an antenna array 206 to generate a single beam 208propagating in a direction that tilts downward and upward in response tochanges in the-voltage division between the voltage sources 204 a and204 b. For example, the beam 208 may be at its highest pointingdirection 208 a when all of the drive power is directed through thevoltage source 204 a, may be at its lowest pointing direction 208 b whenall of the drive power is directed through the voltage source 204 b, maybe at a central pointing direction 208 c when the drive power is dividedequally between the voltage sources 204 a and 208 b, and may varysmoothly between these pointing directions as the power division throughthe voltage sources 204 a and 208 b is varied smoothly.

FIG. 3A is a perspective view of a conceptual design for a double-sided,edge-mounted stripline signal processing module 300. This particularexample includes a first dielectric PC board 302 with an integral groundplane 304 adhered to a second dielectric PC board 306 by a dielectricadhesive 308. The planar dimensions of the PC board dielectric substratesides 302, 306 are coextensive with the common ground plane 304 layer tocreate a double-sided dielectric PC board with a common ground planesandwiched in the middle. Edge connectors 310 are located along a commoninterface edge 312 to permit edge mounting of the module 300 to a socketor another PC board. The first side 302 of the double-sided dielectricPC board carries a first stripline circuit 314, typically a conductivestripline formed into the PC board through a conventional etchingprocess. Similarly, the second side 306 of the double-sided dielectricPC board carries a second stripline circuit 316, again a conductivestripline formed into the PC board through a conventional etchingprocess. As needed, the first and second stripline circuits 314, 316 areconnected to the ground plane 304 layer with ground connections. Thestripline circuits 314, 316 may also be connected to each other with oneor more tap-through connectors 318 that pass through, but areelectrically isolated from, the ground plane 304 layer. However, adesigner could wrap a connector around an edge of the board to create aless elegant but functional electrical connection between the first andsecond stripline circuits 314, 316.

As discussed previously, in certain embodiments the first and secondstripline circuits 314, 316 are non-crossing, and the tap-throughconnectors 318 participate in the implementation of crossovers toimplement a hybrid coupler, hybrid junction, hybrid matrix, or otherorthogonal signal processing module characterized by low-level hybridcomponents connected together through crossovers to create ahigher-level circuit. For example, non-crossing first stage hybridjunctions of a four-by four Butler matrix may be implemented on thefirst side 302 of the double-sided PC board 300. These first stagehybrid junctions include input ports located along the interface edge312, and circuits are laid out to extend away from the interface edge.The second stage hybrid junctions of the four-by four Butler matrix arethen implemented on the second side 306 of the board 300 andinterconnect with the first stage hybrid junctions through crossoverslocated away from the interface edge 312. The second stage hybridjunctions then run back toward the interface edge 312, where theyterminate at output ports located along the interface edge. Thecrossovers required to connect the first and second stage hybridjunctions into the four-by four Butler may be implemented through acombination of tap-through connectors 318 and strategic positioning oroverlaying of the first and second stripline circuits 314, 316 withrespect to each other. This creates a compact, ruggedly constructed,double-sided, edge-mounted four-by-four Butler matrix module, with alleight inputs and output ports located along the interface edge.

FIG. 3B is a perspective view of an alternate conceptual design for adouble-sided, edge-mounted stripline signal processing module 320. Thismodule is similar to the module 300 described with reference to FIG. 3Aexcept that the interface edge 312′ is formed from only a single side306′ of the double-sided PC board. The interface ports may located onboth faces of the PC board 306′ as shown in FIG. 3B, or they may all belocated on one face, in accordance with the manufacturer's designpreference.

FIG. 4 is a perspective exploded view of a double-sided, edge-mountedstripline signal processing module 400. The previously-describedelements including a front-side circuit portion 402, a back-side circuitportion 404, a ground plane 406, edge input and output ports 408, groundconnections 410, and a tap-through connector 412 passing through butelectrically isolated from the common ground plane 406 are shown in anexploded manner for clarity.

FIG. 5A is a functional block diagram of a two-by-four beam formingnetwork 500 that may be used to implement the single-beam verticalelectrical downtilt network 206 shown in FIG. 2. The functional blockdiagram is equivalent to a conventional four-by-four Butler matrix beamforming network with two of the inputs terminated into impedance loadresistors R₁ and R₂. The elements 502 and 504 represent first stagetwo-by-two quadrature (as indicated by the “0/90°” designation) hybridjunction components. The elements 505 and 506 represent second stagetwo-by-two quadrature hybrid junction components, and the elements 510and 512 represent crossovers. There are four output ports (out₁-out₄)but two input ports (in₁ and in₂) because the unnecessary additionalinputs are shunted to ground through impedance matching resistors R1 andR2, as shown in the schematic diagram.

FIG. 5B is a circuit board layout diagram of the back side circuitportion of a double-sided, edge-mounted, stripline signal processingmodule 520 for implementing the two-by-four beam forming network 500shown in FIG. 5A. The second stage hybrid junction 506 is implementedwith sinuous trace elements 522, and the second stage hybrid junction508 is implemented with similar sinuous trace elements 524, to reducethe linear board length running away from the interface 526. FIG. 5Cshows the circuit board layout diagram of the front side circuit portionof the board 530, which carries the first stage hybrid junctions 502 and504 having similar sinuous trace elements. The commonly labeled tappoints (A, B, C, etc.) indicate the locations of tap-through connectorsconnecting the front and back side circuit portions, and the input andoutput ports are labeled. The front and back side portions are broughttogether with the interface edges aligned in a double-sided,edge-mounted configuration. In addition, FIGS. 5B and 5C are laid outwith respect to each other to show the circuit diagrams in a butterflymanner.

The approximate board dimensions of λ_(g) along the interface edge 526and λ_(g)/4 in the direction running away from the interface edge areshow on FIGS. 5B and 5C. For a PC board manufactured from PTFE Teflon®dielectric material exhibiting a dielectric constant equal to 2.2(λ_(r)=2.2), which results in stripline transmission media segmentsexposed to the PC board on one side and exposed to air on the other sideexhibiting an effective dielectric constant of 1.85 (ε_(reff)=1.85).This circuit board design may be implemented for a carrier frequency of1.92 GHz on a double-sided, edge-mounted PC board module that isapproximately λ_(g) (i.e., 4.52 inches or 11.48) cm along the interfaceedge, and is λ_(g)/4 (i.e., 1.13 inches or 2.27 cm) in the directionextending away from the interface edge.

FIG. 6A is a functional block diagram of a two-by-four beam formingcircuit 600, which includes two-by-two quadrature hybrid junctions 602and 604, along with crossovers 606 and 608. FIG. 6B is a circuit boardlayout diagram of a back side portion of a double-sided, edge-mountedstripline signal processing module 610 implementing the two-by-four beamforming circuit shown in FIG. 6A, and FIG. 6C is a circuit board layoutdiagram of the front side portion 620 of that circuit. The beam formingcircuit 600 can be implemented on a PC board module constructed from thesame materials and having the same dimensions as the two-by-four beamforming network 500 described above with reference to FIGS. 5A-C. Inother words, these circuits may be manufactured in an identical mannerexcept that the stripline circuitry is slightly different, asappropriate to implement a different circuit.

FIG. 7A is a functional block diagram of a four-by-four Butler matrixbeam forming module 700, which includes first stage two-by-twoquadrature hybrid junctions 702 and 704, second stage two-by-twoquadrature hybrid junctions 706 and 708, phase shifters 710 and 712, andcrossovers 714 and 716. FIG. 7B is a circuit board layout diagram of theback side of a double-sided, edge-mounted stripline signal processingmodule 720 implementing the four-by-four Butler matrix shown in FIG. 7A,and FIG. 7C is the circuit board layout diagram of the back side 722 ofthat circuit. The four-by-four Butler matrix 700 can be implemented on aPC board module constructed from the same materials and having the samedimensions as the two-by-four beam forming networks 500 and 600described above with reference to FIGS. 5A-C and FIGS. 6A-C,respectively.

FIG. 8A is a functional block diagram of a four-by-four monopulsecomparator module 800, which includes first stage two-by-two quadraturehybrid junctions 802 and 804, second stage quadrature hybrid junctions806 and 808, and crossovers 810 and 812. The hybrid junctions 802 and804 are used in combination with phase offset shifters 812 and 814 toeffectively to produce the functional equivalent characteristics of atwo-by-two “magic-T” (0°/180°) hybrid junction. It is well known tothose familiar with the art that, for example, a “rat-race” 0°/180°hybrid junction can be used in place of the hybrid junction 802 andphase offset shifter 812. FIG. 8B is a circuit board layout diagram ofthe back side portion of a double-sided, edge-mounted stripline signalprocessing module 820 implementing the four-by-four monopulse comparatorcircuit shown in FIG. 8A, and FIG. 8C is the circuit board layoutdiagram of the front side 822 portion of that circuit. The four-by-fourmonopulse comparator circuit 800 can be implemented on a PC board moduleconstructed from the same materials and having the same dimensions asthe two-by-four beam forming networks 500 and 600 described above withreference to FIGS. 5A-C and FIGS. 6A-C, respectively, and thefour-by-four Butler matrix 700 described above with reference to FIGS.7A-C.

FIG. 9 is a functional block diagram of an eight-by-eight Butler matrixmodule 900, which includes a first stage 902 including a firstfour-by-four “quasi-Butler” matrix 904 and a second four-by-four“quasi-Butler” matrix 906. The circuit 900 also includes a second stage908 including four hybrid junctions 910 a-d. The first “quasi-Butler”matrix 904 includes first stage quadrature hybrid junctions 912 and 914,second stage quadrature hybrid junctions 916 and 918, a crossover 920,and a 67.5° phase offset shifter 921, and a 22.50 phase offset shifter936. Similarly, the second “quasi-Butler” matrix 906 includes firststage quadrature hybrid junctions 922 and 924, second stage quadraturehybrid junctions 926 and 928, a crossover 930, and a 67.5° phase offsetshifter 931, and a 22.5° phase offset shifter 937. Additional crossovers940 and 942 and 45° phase shifters 932, 934, 935, and 924 connect thefirst stage 902 to the second stage 908, with further crossovers 944,946, 948, and 950 connecting the hybrid junctions of the second stage908 to the output ports.

FIG. 10A is a circuit board layout diagram of the back side circuitportion 1000 of a double-sided, edge-mounted stripline signal processingmodule implementing the eight-by-eight Butler matrix circuit shown inFIG. 9, and FIG. 10B shows the front side circuit portion of thatmodule. As in the previous double-sided circuit board illustrations,FIGS. 10A and 10B are illustrated in a butterfly manner with commondesignation (e.g., A, B, C, etc.) identifying the tap-throughconnectors, which typically participate in the implementation of thecrossovers. FIGS. 10A-10B also illustrate the use of sinuous trace legs,as exemplified by the sinuous trace leg 1004, to reduce the board sizein the direction extending away from the interface edge 1006. The planarboard dimensions in multiples of λ_(g) are also shown.

FIG. 11A is a conceptual diagram of an edge-mounted modular striplinesignal processing network 1100 for implementing an eight-by-eight Butlermatrix from two four-by-four “quasi-Butler” matrix modules 1102 and 1104and a third module 1106 implementing four hybrid junctions edgeconnected to a motherboard 1108. Of course, one or more of thesemodules, or additional functionality, could be implemented on themotherboard 1108. FIG. 11B is a functional block diagram of aneight-by-eight Butler matrix similar to the diagram of FIG. 9, but inthis example illustrating how the signal processing functions aredivided among the modules shown in FIG. 11A. Specifically, the firstfour-by-four “quasi-Butler” matrix 904 is implemented on the firstmodule 1102, the second four-by-four “quasi-Butler” matrix 906 isimplemented on the second module 1104, and the four hybrid junctions ofthe second stage 908 are implemented on the first module 1106. Thesethree modules are edge-mounted to and interconnected through themotherboard 1108 to provide a multi-module alternative for implementingthe same eight-by-eight Butler matrix described with reference to FIGS.10A-10C, which his implemented as a single double-sided, edge-mountedplanar module.

FIG. 12 is a conceptual diagram of tree-type stripline signal processingnetwork 1200 comprising a “tree” type system of daughter boards 1204,1206, 1208, 1210, and 1212 edge mounted to a mother board 1202. That is,the modular signal processing architecture illustrated at a relativelysimple level in FIGS. 11A-11B may be extended in a straightforwardmanner to create more complex processing systems to drive higher-ordernetworks, such as a 64-by-64 Butler matrix, 128-by-128 Butler matrix, amulti-level high-power hybrid matrix amplifier, and so forth. Thesestripline signal processing engines, in turn, provide the signalprocessing infrastructure for complex systems, such as multi-beamDoppler radars, multi-beam missile tracking and defense systems,multi-beam satellite reconnaissance systems, and many other devicesemploying the modular signal processing architecture illustrated by theexemplary embodiments of the invention described above.

FIG. 13 illustrates a modular stripline signal processing network 1300including daughter boards 1302, 1304, and 1306 edge mounted to motherboard 1308 using separable blind-mate coaxial connectors exemplified bythe connector 1310, 1320. Using separable connectors 1310 and 1312 toconnect the boards together facilitates installation and removal of theboards for modular construction and maintenance purposes. It will beappreciated that additional support structures, such as side railsupports and board lock-down mechanisms, as are well know in the art,may be employed to increase the physical integrity of the constructedunit.

FIG. 14 is a logic flow diagram illustrating a process 1400 fordesigning a modular stripline signal processing network. The followingdescription will refer to the four-board structure implementing theeight-by-eight Butler matrix shown in FIGS. 11A-B as a simple butillustrative example of the network design process. In step 1402, thecircuit designer defines the requirements of the network, such as aneight-by-eight Butler matrix for the example shown in FIGS. 11A-B. Step1402 is followed by step 1404, in which the circuit designer breaks downthe overall network into zones. In the eight-by-eight Butler matrixexample shown in FIGS. 11A-B, these zones include the first four-by-four“quasi-Butler” matrix 904 as a first zone, the second four-by-four“quasi-Butler” matrix 906 as a second zone, and the four hybridjunctions 908 as a third zone. Step 1404 is followed by step 1406, inwhich the circuit designer defines modules to implement the zones thatare properly sized for the desired module sizes. Step 1406 is followedby step 1408, in which the circuit designer designs front and backcircuit portions, along with tap-through connections as appropriate,that overlay each other to implement the circuits in a double-sidedmanner, preferably with non-crossing circuit portions on each side ofthe board. Step 1408 is followed by step-1410, in which the circuitdesigner designs the modules to implement the required functionalitywhile meeting applicable module constraints.

This result of this process is illustrated by the modular board designshown in FIGS. 5A-C, 6A-C, 7A-C, 8A-C, and 10A-B, in which each moduleis laid out in a double-sided, edge-connected format employingnon-crossing circuit portions on each side of the board and tap-throughconnections to implement crossovers. Step 1410 is followed by step 1412,in which the circuit designer designs the modular assembly. In theeight-by-eight Butler matrix for the example shown in FIGS. 11A-B, thiscorresponds to edge connecting the modules 1102, 1104 and 1106 to themother board 1108 to create a complete modular design. It will beappreciated that the four-board modular design of the eight-by-eightButler matrix shown in FIGS. 11A-B is but one relatively simple exampleof a design technique enabled by the present invention that may be useddesign and construct a wide range of stripline signal processingmachines within the class of double-sided, edge-mounted printed circuit(PC) modules and the associated modular network architecture.

The stripline modules described above with reference to FIGS. 3A-10B areof the type commonly referred to as “microstrip,” in which the striplinetransmission media segments are exposed to a dielectric material on oneside and air on the other. It should be understood that any of thestripline circuits described in this specification may alternatively beconfigured as tri-plate stripline modules, in which the striplinetransmission media segments are exposed to a dielectric material on bothsides. This is typically accomplished by adding dielectric covers withouter ground plates over the air-exposed stripline circuits of themicrostrip configurations. The result is a multi-layer double-sidedstripline module including a first outer ground plane layer, followed bya dielectric layer, followed by a first stripline circuit layer,followed by a dielectric layer, followed by a center ground plane layer,followed by aodielectric layer, followed by a second stripline circuitlayer, followed by a dielectric layer, followed by a second outer groundplane layer.

For example, FIG. 15A is a perspective exploded view of a tri-platestripline module 1500 for implementing a two-by-four beam formingnetwork similar to the circuit shown in FIG. 6A-C. To create thetri-plate stripline structure, a first dielectric cover 1501 with anouter ground plane 1502 has been added over a first microstrip circuitboard 1503, which typically includes a dielectric PC board with astripline circuit 1504 (shown in FIG. 15C) on one side and a groundplane 1505 adhered to the other side. In addition, a second dielectriccover 1506 with an outer ground plane 1507 has been added over a secondmicrostrip circuit board 1508, which typically includes a dielectric PCboard carrying a stripline circuit 1509. That is, the tri-platestripline module 1500 contains an equivalent of the two-by-four beamforming network similar to the circuit shown in FIG. 6A-B (representedby elements 1503 and 1508 in FIG. 15A) with additional dielectric covers1501 and 1506, which each have outer ground planes 1502 and 1507,respectively. The additional dielectric cover with an outer groundplanes shield the stripline circuits from radiating losses andinterference. FIG. 15C shows a side view of layer 1503 carrying thefirst stripline circuit 1504, FIG. 15C shows a side view of layer 1508carrying the second stripline circuit 1509, FIG. 15B shows an assembledperspective view of the tri-plate stripline module 1500.

In this particular module, the first stripline circuit 1504 shown inFIG. 15C is similar to the microstrip circuit 610 of the two-by-fourbeam forming network similar to the circuit shown in FIG. 6B except thatthe lengths and widths of the stripline segments are adjusted to accountfor the different dielectric exposed to the stripline segments (i.e.,air on one side of the stripline segments and a dielectric substrate onthe other side of the stripline segments in the embodiment of FIG. 6A-C,versus a dielectric material on both sides of the stripline segments inthe embodiment of FIGS. 15A-D). Similarly, the second stripline circuit1509 shown in FIG. 15B is similar to the microstrip circuit 612 of thetwo-by-four beam forming network shown in FIG. 6C except that thelengths and widths of the stripline segments are adjusted to account forthe different dielectric exposed to the stripline segments. Thoseskilled in the art will understand how to adjust the lengths and widthsof the stripline segments to account for this change in the effectivedielectric constant for the segments. Although this particular moduleimplements a two-by-four beam forming network, any of the double-sidedstripline circuits described in this specification may be implemented ina similar tri-plate stripline configuration.

FIG. 16A is a functional block diagram of a two-by-one diplexer filtercircuit 1600, which includes two-by-two quadrature hybrid junctions 1602and 1604, along with phase offset shifters 1606 and 1608 and a length oftransmission line 1610 that is producing an additional signal delay inone signal path. FIG. 6B is a circuit board layout diagram of a backside portion of a double-sided, edge-mounted stripline signal processingmodule 1620 implementing the two-by-one diplex filter circuit shown inFIG. 16A, and FIG. 16C is a circuit board layout diagram of the frontside portion 1622 of that circuit. The diplexer filter circuit 1600 canbe implemented on a PC board module constructed from the same materialsand having smaller dimensions as the two-by-four beam forming network500 described above with reference to FIGS. 5A-C. In other words, thesecircuits may be manufactured in an identical manner except that thestripline circuitry is slightly different, as appropriate to implement adifferent circuit.

In view of the foregoing, it will be appreciated that present inventionprovides significant improvements in stripline signal processing networkdesign. It should be understood that the foregoing relates only to theexemplary embodiments of the present invention, and that numerouschanges may be made therein without departing from the spirit and scopeof the invention as defined by the following claims.

1-37. (canceled)
 38. A signal processing module configured to perform asignal processing operation on signals propagating through the module,comprising: a front-side microstrip circuit portion having a conductiveprinted circuit side exposed to air on a first side and exposed to afirst dielectric substrate on an opposing side; a back-side microstripcircuit portion having a conductive printed circuit side exposed to airon a first side and exposed to a second dielectric substrate on anopposing side; and a ground plane sandwiched between the front-side andthe back-side microstrip circuit portions.
 39. The signal processingmodule of claim 38, further comprising: one or more tap-throughconnectors electrically connecting the printed circuit side of thefront-side microstrip circuit portion to the printed circuit side of theback-side microstrip circuit portion; the tap-through connectorsextending through and electrically insulated from the ground plane; andwherein the printed circuit sides of the front-side and back-sidecircuit portions, as connected by the tap-through connectors, form anintegral double-sided microstrip circuit.
 40. The signal processingmodule of claim 39, wherein the integral double-sided microstrip circuitcomprises an orthogonal signal processing network implementing acrossover defined by the printed circuit sides of the front-side andback-side circuit portions and the tap-through connectors.
 41. Thesignal processing module of claim 40, wherein the orthogonal signalprocessing network comprises a Butler matrix circuit signal processingnetwork.
 42. The signal processing module of claim 40, wherein theorthogonal signal processing network implements a circuit selected fromthe group consisting of: a two-by-four beam steering circuit; a diplexerfilter circuit comprising at least three ports; a four-by-four Butlermatrix circuit; an eight-by-eight Butler matrix circuit; and a monopulsecomparator circuit.
 43. The signal processing module of claim 42,wherein: the signal processing module defines an interface edge with oneor more input ports and one or more output ports located at theinterface edge; and the integral double-sided microstrip circuitperforms the signal processing operation on signals received by the atthe input ports, propagating through the integral double-sidedmicrostrip circuit and delivered to the output ports.
 44. A signalprocessing module configured to perform a signal processing operation onsignals propagating through the module, comprising: a first ground planecarried by a first dielectric substrate; a front-side microstrip circuitportion having a conductive printed circuit side exposed to thedielectric substrate carried by the first ground plane on a first side,and having a dielectric material on an opposing side; a second groundplane carried by a second dielectric substrate; a back-side microstripcircuit portion having a conductive printed circuit side exposed to thedielectric substrate carried by the second ground plane on a first side,and having a dielectric material on an opposing side; and a third groundplane sandwiched between the dielectric material sides of the front-sideand the back-side microstrip circuit portions.
 45. The signal processingmodule of claim 44, wherein: the signal processing module definesan-interface edge with one or more input ports and one or more outputports located at the interface edge; and the integral double-sidedmicrostrip circuit performs the signal processing operation on signalsreceived by the at the input ports, propagating through the integraldouble-sided microstrip circuit and delivered to the output ports. 46.The signal processing module of claim 45, further comprising: one ormore tap-through connectors electrically connecting the printed circuitside of the front-side microstrip circuit portion to the printed circuitside of the back-side microstrip circuit portion; the tap-throughconnectors extending through and electrically insulated from the thirdground plane; and wherein the printed circuit sides of the front-sideand back-side circuit portions, as connected by the tap-throughconnectors, form an integral double-sided microstrip circuit.
 47. Thesignal processing module of claim 45, wherein the integral double-sidedmicrostrip circuit comprises an orthogonal signal processing networkimplementing a crossover defined by the printed circuit sides of thefront-side and back-side circuit portions and the tap-throughconnectors.
 48. The signal processing module of claim 47, wherein theorthogonal signal processing network comprises a Butler matrix circuitsignal processing network.
 49. The signal processing module of claim 47,wherein the orthogonal signal processing network implements a circuitselected from the group consisting of: a two-by-four beam steeringcircuit; a diplexer filter circuit comprising at least three ports; afour-by-four Butler matrix circuit; an eight-by-eight Butler matrixcircuit; and a monopulse comparator circuit.
 50. A signal processingmodule configured to perform a signal processing operation on signalspropagating through the module, comprising: a multi-layer double-sidedstripline PC circuit board comprising a series of thin, flat parallellayers defining an interface edge with one or more input ports and oneor more output ports located at the interface edge; the PC circuit boardcomprising: a first layer comprising a first microstrip transmissionmedia circuit portion exposed to air on one side and a second layer onits other side; the second layer comprising a first dielectric substrateon which the first microstrip transmission media is printed to form afirst PC board, the second layer exposed to the first layer on one sideand a third layer on its other side; the third layer comprising a commonground plane exposed to an adhesive layer on one side and the second ora fourth layer on its other side; the fourth layer comprising a seconddielectric substrate on which a second microstrip transmission media isprinted to form a second PC board, the fourth layer exposed to a fifthlayer on one side and the adhesive layer or the ground plane on itsother side; and the fifth layer comprising a second microstriptransmission media circuit portion exposed to air on one side and afourth layer on its other side.
 51. The signal processing module ofclaim 50, further comprising: one or more tap-through connectorselectrically connecting the first layer to the fifth layer, extendingthrough the second, third and fourth layers, and electrically insulatedfrom the ground plane; wherein the first and second microstriptransmission media circuit portions, as connected by the tap-throughconnectors, form an integral double-sided microstrip circuit with theground plane sandwiched in the middle; and wherein the integraldouble-sided microstrip circuit performs the signal processing operationon signals received by the at the input ports, propagating through theintegral double-sided microstrip circuit and delivered to the outputports.
 52. The signal processing module of claim 51, wherein theintegral double-sided microstrip circuit comprises an orthogonal signalprocessing network implementing a crossover defined by the first andsecond microstrip transmission media circuit portions and thetap-through connectors.
 53. The signal processing module of claim 51,wherein the orthogonal signal processing network comprises a Butlermatrix circuit signal processing network.
 54. The signal processingmodule of claim 52, wherein each network module implements a circuitselected from the group consisting of: a two-by-four beam steeringcircuit; a diplexer filter circuit comprising at least three ports; afour-by-four Butler matrix circuit; an eight-by-eight Butler matrixcircuit; and a monopulse comparator circuit.
 55. The signal processingmodule of claim 50, further comprising a third microstrip transmissionmedia circuit portion carried on the side of second layer opposing thefirst layer.